In the prior art, rubber compositions having a base material of acrylic rubber are often used in hoses that require heat resistance, oil resistance, and cold resistance, such as in oil system hoses or air system hoses and the like for automobiles. In general, acrylic rubber has good heat resistance and oil resistance and also has good compression set resistance. As a result, when used in hoses, it has excellent sealing quality at the hose connection part.
When an acrylic rubber composition is used in a heat-resistant hose that is used under extreme conditions, such as in an air hose for a supercharger in a turbocharger assembly vehicle, if the connecting pipe is made of aluminum (or its alloy), the acrylic rubber composition often becomes fixed to the aluminum. The replacement operation of the heat-resistant hose has therefore been difficult (henceforth “aluminum fixing” refers to this fixing phenomenon).
The reason for the above aluminum fixing problem is thought to be the following. Aluminum is readily oxidized by the oxygen in the air to form alumina. Further, in the presence of water, alumina readily forms a hydroxide. This hydroxide and the rubber material react, which causes aluminum fixing.
In the prior art, in order to prevent aluminum fixing, in the invention described in Japanese Laid-Open Patent Publication Number 2001-2877 for example, an acryl-silicon copolymer is added to the acrylic rubber. In the invention described in Japanese Laid Open Patent Publication Number H6-88005, a phosphate ester plasticizer is added to the acrylic rubber, or a fatty acid processing aid or a metal soap compound is mixed into the acrylic rubber. Furthermore, in the invention described in Japanese Laid Open Patent Publication Number H5-148476, by adding a silicon processing aid, there is an effect of surface covering.
However, with the prior art described above, apart from their effectiveness in preventing aluminum fixing, the above strategies result in normal state physical properties which are inferior for acrylic rubber. In addition, there can be reduced heat resistance and compression set resistance which are characteristics of the acrylic rubber, or there may be bleeding of the mixing agents.
An object of the present invention is to provide an acrylic rubber composition which effectively prevents aluminum fixing while still retaining the physical properties and superior characteristics of acrylic rubber. A further object of the present invention is to provide a heat-resistant hose which uses this acrylic rubber composition in surfaces that join with aluminum or aluminum alloy members.